Gelating agent for alkaline cell and alkaline cell

ABSTRACT

A gelating agent for an alkaline cell is a cross-linked polymer (A) comprising (meth)acrylic acid and/or its alkali metal salt as a main constituent monomer unit and obtained by an aqueous solution polymerization or a reversed phase suspension polymerization and satisfies the following required conditions (1), (2). The gelating agent has good draining property, satisfactorily high speed charging property of the alkaline electrolytic solution and is therefore effective to produce cells with little unevenness of the charging amount of the electrolytic solution and having uniform quality by mass production and an alkaline cell using the gelating agent is provided with durable discharge time and remarkably excellent impact resistance for a long duration. The said required conditions are required condition (1); that the gelating agent contains 50% by weight or more of a particle whose swollen particle size becomes 300 to 4,000 μm when the gelating agent is swollen in an aqueous potassium hydroxide solution of 40% by weight concentration and required condition (2); that the aqueous potassium hydroxide solution of 40% by weight concentration containing 3% by weight of the gelating agent has 0 to 20 mm stringiness.

TECHNICAL FIELD

The present invention relates to a gelating agent for an alkaline celland an alkaline cell. More particularly, the present invention relatesto a gelating agent of a gel type anode for an alkaline cell comprisingthe anode containing an alkaline electrolytic solution and a zinc powderas a mainly component and using the gelating agent and also to analkaline cell using the gelating agent.

PRIOR ART

Conventionally, mainly used for an anode of an alkaline cell is amixture containing an alkaline electrolytic solution in a highconcentration (an aqueous high concentration potassium hydroxidesolution, if necessary, containing zinc oxide) and a zinc powder and/ora zinc alloy powder and for the purpose of preventing the precipitationof the zinc powder in the alkaline electrolytic solution, an anodeproposed as the gelating agent are water-absorptive resin materials withrelatively large particle size and comprising poly(meth)acrylic acidsand their salts made insoluble by cross-linking agents [(i) JapanesePatent No. 8-28216, (ii) Japanese Patent No. 8-12775, (iii) JapanesePatent Laid-Open No. 10-50303, and the like).

However, these gelating agents are not necessarily satisfactory inprevention of precipitation of a zinc powder, liquid leakage from acell, and drain of gelating agents, in productivity of cells, and thelike.

SUMMARY OF THE INVENTION

Inventors of the present invention have enthusiastically madeinvestigations taking the above described situation into considerationand surprisingly found that gelating agents whose stringiness, particlesize and the like are defined within specified ranges have improvedproperties in the above described disadvantages and provide remarkablydesirable results in the discharging property, the life, the impactresistance, the workability, and the like of a cell and thus achievedthe present invention.

A first purpose of the present invention is to provide a gelating agentproviding remarkably excellent effects on sustainability of electricdischarge and impact resistance of an alkaline cell.

A second purpose of the present invention is to provide a gelating agentof an alkaline cell capable of providing an excellent property instringiness of an alkaline electrolytic solution and dealing with thehigh speed packing of the alkaline electrolytic solution.

A third purpose of the present invention is to provide a gelating agentof an alkaline cell effective to manufacture a cell with uniform qualitywith little unevenness in the packed amount of an electrolytic solutioneven in the case of mass production.

A fourth purpose of the present invention is to provide a gelating agentof an alkaline cell capable of preventing hydrogen gas evolution even ifit is brought into contact with a zinc powder in an electrolyticsolution and having no probability of causing leakage of an electrolyticsolution and damaging a cell attributed to the inner pressure of thecell.

A fifth purpose of the present invention is to provide an alkaline cellusing such a gelating agent.

In other words, the present invention provides the following gelatingagents [1] to [14] and an alkaline cell [15].

[1] Gelating Agent:

A swelling-in-water type gelating agent of a cross-linked polymer (A)comprising (meth)acrylic acid and/or its alkali metal salt as a mainconstituent monomer unit and obtained by an aqueous solutionpolymerization or a reversed phase suspension polymerization, whereinthe gelating agent for an alkaline cell satisfies the following requiredconditions (1), (2):

required condition (1); that the gelating agent contains 50% by weightor more of a particle whose swollen particle size becomes 300 to 4,000μm when the gelating agent is swollen in an aqueous potassium hydroxidesolution of 40% by weight concentration; and

required condition (2); that the aqueous potassium hydroxide solution of40% by weight concentration containing 3% by weight of the gelatingagent has 0 to 20 mm stringiness.

[2] Gelating Agent:

A gelating agent for an alkaline cell satisfies the required condition(3) in addition to the foregoing conditions (1), (2):

required condition (3); that the aqueous potassium hydroxide solution of40% by weight concentration containing 3% by weight of the gelatingagent has viscosity of 50 to 1,000 Pa.s at 40° C. after one day andsixty days.

[3] Gelating Agent:

A gelating agent for an alkaline cell satisfies the required condition(4) in addition to the foregoing conditions (1), (2) or (1) to (3):

required condition (4); that the gelating agent contains 0 to 15 ppm ofa metal with a lower ionization tendency than zinc.

[4] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [1] containing the swollen particle satisfying the foregoing requiredcondition (1) whose particle size is 500 to 2,000 μm.

[5] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [1] containing 0 to 30% by weight of soluble components in an aqueouspotassium hydroxide solution of 10% by weight concentration when thegelating agent is swollen in the said aqueous solution.

[6] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [1], wherein the forgoing polymer (A) is a cross-linked polymer with5,000 to 1,000,000 average polymerization degree and cross-linked by anallyl ether type cross-linking agent (b) having 2 to 10 of allyl groupsin a molecule and added in 0.05 to 1.0% by weight to the total weight ofthe (meth)acrylic acid and/or its alkali metal salt.

[7] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [6], wherein the forgoing agent (b) has 3 to 10 of allyl groups in amolecule and 1 to 5 of hydroxyl groups in a molecule.

[8] a Gelating Agent:

A swelling-in-water type gelating agent of a cross-linked polymer (A′)obtained by cross-linking a polymer which comprises (meth)acrylic acidand/or its alkali metal salt as a main constituent monomer unit, has5,000 to 1,000,000 average polymerization degree and is produced by anaqueous solution polymerization or a reversed phase suspensionpolymerization, with an allyl ether type cross-linking agent (b) having2 to 10 of allyl groups in a molecule and added in 0.05 to 1.0% byweight to the total weight of the (meth)acrylic acid and/or its alkalimetal salt, wherein the gelating agent for an alkaline cell satisfiesthe following required conditions (1) to (4): required condition (1);that the gelating agent contains 50% by weight or more of a particlewhose swollen particle size becomes 300 to 4,000 μm when the gelatingagent is swollen in an aqueous potassium hydroxide solution of 40% byweight concentration; required condition (2); that the aqueous potassiumhydroxide solution of 40% by weight concentration containing 3% byweight of the gelating agent has 0 to 20 mm stringiness; requiredcondition (3); that the aqueous potassium hydroxide solution of 40% byweight concentration containing 3% by weight of the gelating agent hasviscosity of 50 to 2,000 Pa.s at 40° C. after one day and sixty days;and required condition (4); that the gelating agent contains 0 to 15 ppmof a metal with a lower ionization tendency than zinc.

[9] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [1], wherein the polymer (A) is obtained by polymerizing a monomercomprising mainly (meth)acrylic acid and/or its alkali metal salt withneutralization degree of 0 to 30% by mole and neutralizing the polymerbased on necessity after polymerization.

[10] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [1] obtained by carrying out permeation drying and/or ventilationdrying based on necessity after segmentation of water-containing gel inthe process of drying the water-containing gel of the polymer (A) orcarrying out vacuum drying and/or ventilation drying after solid-liquidseparation of the water-containing gel.

[11] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [8] containing the swollen particle satisfying the foregoing requiredcondition (1) whose particle size is 500 to 2,000 μm.

[12] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [8] containing 0 to 30% by weight of soluble components in an aqueouspotassium hydroxide solution of 10% by weight concentration when thegelating agent is swollen in the said aqueous solution.

[13] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [8], wherein the polymer (A′) is obtained by polymerizing a monomercomprising mainly (meth)acrylic acid and/or its alkali metal salt withneutralization degree of 0 to 30% by mole and neutralizing the polymerbased on necessity after polymerization.

[14] Gelating Agent:

A gelating agent for an alkaline cell is the gelating agent as definedin [8] obtained by carrying out permeation drying and/or ventilationdrying based on necessity after segmentation of water-containing gel inthe process of drying the water-containing gel of the polymer (A′) orcarrying out vacuum drying and/or ventilation drying after solid-liquidseparation of the water-containing gel.

[15] Alkaline Cell:

An alkaline cell using a gelating agent of [1] to [14].

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section figure showing one example of an alkalinecell of the present invention.

The symbols denote as follows:

1 a cathode terminal plate

2 a shrinkage tube

3 a cathode agent (MnO₂+carbon)

4 an outer can

5 a separator

6 a current collector rod

7 a gasket

8 an anode terminal plate

9 a gel anode

DETAILED DESCRIPTION OF THE INVENTION Cross-linked Polymer

In the present invention, the cross-linked polymer (A) to be used as agelating agent for an alkaline cell is preferable to be obtained bypolymerizing mainly (meth)acrylic acid (alkali metal salt) (denotingacrylic acid and/or methacrylic acid and/or their alkali metal salts andhereinafter the same) by an aqueous solution polymerization method or areversed suspension polymerization method in the presence of an allylether type copolymerizable cross-linking agent (b).

In this case, (meth)acrylic acid means acrylic acid and/or methacrylicacid and their metal salts are neutralized acrylic acid and/ormethacrylic acid with alkali metals such as potassium, sodium, lithiumand the like.

In the present invention, neutralization of (meth)acrylic acid with analkali metal may be carried out to give incompletely neutralized orneutralized cross-linked polymer (A) since the gelating agent of thepresent invention is to be used in an aqueous alkaline solution in ahigh concentration, however it is preferable to be carried out partiallyor entirely for (meth)acrylic acid for the purpose to lower theviscosity and the dispersibility of the polymer (A) and to improve theworkability in production of the polymer (A) and the like.

In the case (meth)acrylic acid is neutralized based on necessity,generally an alkali metal hydroxide such as potassium hydroxide, sodiumhydroxide, lithium hydroxide, and the like or their aqueous solutionsmay be added to (meth)acrylic acid in monomer stage beforepolymerization or to a water-containing gel after polymerization,however, in the case of using an allyl ether type copolymerizablecross-linking agent (b), which will be described later, the agent isinsufficient in water-solubility, so that if polymerization is carriedout in high neutralization degree of (meth)acrylic acid, it is sometimesimpossible to obtain the cross-linked polymer (A) with defined physicalproperties even with addition of a prescribed amount of thecross-linking agent (b) attributed to isolation of the cross-linkingagent (b) from the aqueous monomer solution and impossibility of theprescribed cross-linking reaction. Hence it is preferable to adjust theneutralization degree by adding an alkali metal hydroxide to awater-containing gel based on necessity after polymerization of(meth)acrylic acid whose neutralization degree is controlled to be 0 to30% by mole.

The final neutralization degree of (meth)acrylic acid of the gelatingagent of the present invention is preferably 30 to 100% and furtherpreferably 50 to 90%.

In the present invention, in the case of production of the cross-linkedpolymer (A), the aqueous solution polymerization and/or the reversedphase suspension polymerization of mainly polymers of (meth)acrylic acid(alkali metal salts) as monomers is carried out and if necessary, amonoethylenic unsaturated monomer copolymerizable with (meth)acrylicacid (alkali metal salts) may be copolymerized. The monoethylenicunsaturated monomer is not particularly restricted as long as themonomer is polymerizable, and examples are anionic ethylenic unsaturatedmonomers, e.g. a monomer containing carboxylic acid (salt) group such asmaleic acid (alkali metal salt), fumaric acid (alkali metal salt),itaconic acid (alkali metal salt) and the like, a monomer containingsulfonic acid (salt) group such as acrylamide-2-methylpropanesulfonicacid (alkali metal salt), sulfoalkyl (meth)acrylate, stylenesulfonicacid (alkali metal salt) and the like; nonionic water soluble ethylenicunsaturated monomers, e.g. (meth)acrylamide, N-(1-3C)alkyl-substituted(meth)acrylamide, [N-methylacrylamide, N,N-dimethylacrylamide and thelike], N-vinylacetamide, monohydroxy(1-3C)alkyl mono(meth)acrylate,polyethylene glycol (polymerization degree: 2 to 100)mono(meth)acrylate, polypropylene glycol (polymerization degree: 2 to100) mono(meth)acrylate, methoxypolyethylene glycol (polymerizationdegree: 2 to 100) mono(meth)acrylate, and the like; and othermonoethylenic unsaturated monomers such as (1-5C)alkyl (meth)acrylate,vinyl acetate and the like. These ethylenic unsaturated monomers may beused in combination of two or more of them within a prescribed range ofthe amount.

The additional amount of an ethylenic unsaturated monomer other thanthese (meth)acrylic acid and/or their alkali metal salts is generally 0to 50% by weight and preferably 0 to 30% by weight to the weight of the(meth)acrylic acid (alkali metal salt) at the time of polymerization.

In this invention, at the time of production of the polymer (A), inorder to lower the stringiness in a high concentration alkalineelectrolytic solution and to stabilize the gel in alkaline state, it ispreferable to use an allyl ether type copolymerizable cross-linkingagent (b) having two or more allyl groups in a molecule.

As the allyl ether type copolymerizable cross-linking agent (b), usableare, for example, cross-linking agents (b1) having two allyl groups andno hydroxy group in a molecule represented by (2-5C) alkyleneglycoldiallyl ether, polyethylene glycol diallyl ether (Mw: 100 to 4,000) andthe like; cross-linking agents (b2) having two allyl groups and 1 to 5hydroxy groups in a molecule and represented by glycerol diallyl ether,trimethylolpropane diallyl ether, pentaerythritol diallyl ether,polyglycerol diallyl ether, and the like; cross-linking agents (b3)having 3 to 10 allyl groups and no hydroxy group in a molecule andrepresented by trimethylolpropane triallyl ether, glycerol triallylether, pentaerythritol tetraallyl ether, tetraallyloxyethane and thelike; and cross-linking agents (b4) having 3 to 10 allyl groups and 1 to5 hydroxy groups in a molecule and represented by pentaerythritoltriallyl ether, diglycerol triallyl ether, polyglycerol (polymerizationdegree 3 to 13) polyallyl ether and the like. These allyl ether typecross-linking agents may be used in combination of two or more of them.

Among the allyl ether type cross-linking agents (b), these (b4) arepreferable since they have excellent compatibility with acrylic acidand/or alkali metal salts in the aqueous solution polymerization and/orthe reversed phase suspension polymerization owing to the possession of1 to 5 hydroxy groups and 3 to 10 allyl groups, and they are capable ofcarrying out efficient cross-linking as to cover the lowcopolymerization property, which is intrinsic property of allyl groups,attributed to the existence of a large number of allyl groups.

In the present invention, although it depends on the types of thecross-linking agents to be used and the average polymerization degree of(meth)acrylic acid (alkali metal salts), the additional amount of theagent (b) is generally 0.05 to 2% by weight and preferably 0.1 to 1% byweight to the (meth)acrylic acid (alkali metal salts). If the additionalamount is 0.05% by weight or higher, it is possible to lower thestringiness of the gelating agent in a produced aqueous alkalinesolution containing the gelating agent, to improve the stability of thegelating agent in alkaline conditions, and to prevent deterioration ofthe viscosity with the lapse in time. On the other hand, if theadditional amount is 2% by weight or lower, it is possible to preventthe cross-linking density from becoming too high and the absorptionamount of the aqueous alkaline solution from lowering, so that theviscosity of the aqueous alkaline solution mixed with the gelating agentis not lowered and the isolation of the alkaline electrolytic solutioncan be prevented.

In the present invention, as described above, the allyl ether typecross-linking agent (b) with a stable cross-linking structure under ahigh concentration alkaline condition is preferable as a cross-linkingagent and may be used in combination with another cross-linking agent(c) other than allyl ether type ones for the purpose to improve thedispersibility of the gelating agents in an aqueous alkaline solutionand improve the absorption speed, although the cross-linking agentscommonly used for water-absorptive resin, e.g. ester type cross-linkingagents such as trimethylolpropane triacrylate, amide typecopolymerizable cross-linking agents such as methylenebisacrylamide,cross-linking agents reactive with carboxylic acids such as ethyleneglycol diglycidyl ether, are scarcely effective to lower the stringinessof the polymers under strongly alkaline conditions and to improve thelong-term stability of gels since their cross-linking structure iseasily decomposed under the strongly alkaline conditions.

As these other cross-linking agents (c), examples are copolymerizablecross-linking agents (c1) having 2 to 10 functional groups in a moleculeand represented by N,N′-methylenebisacrylamide, ethylene glycoldi(meth)acrylate, trimethylolpropane di(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritol di(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerithritol tetra(meth)acrylateand the like and cross-linking agents (c2) reactive with carboxylicacids and represented by polyvalent glycidyl compounds such as ethyleneglycol diglycidyl ether, polyvalent isocyanate compounds such as4,4′-diphenylmethane diisocyanate, polyvalent amine compounds such asethylene diamine, polyvalent alcohol compounds such as glycerin and thelike.

In the case these reactive cross-linking agents (c2) are used, it iscommon to promote the cross-linking reaction by heating generally at 100to 230° C. and preferably 120 to 160° C. in any stage aftercross-linking agent addition. Further, these reactive cross-linkingagents may be used in combination of two or more kinds of them within aprescribed range of the amount and further in combination with thecopolymerizable cross-linking agents (c1).

The additional amount of these other cross-linking agents (c) to beadded based on the necessity is preferably 0 to 0.5% by weight and morepreferably 0 to 0.3% by weight to the weight of (meth)acrylic acid(alkali metal salts).

Production Method of Cross-linked Polymer

An aqueous solution polymerization method for carrying outpolymerization of an aqueous monomer solution mainly containing(meth)acrylic acid (alkali metal salts) by adding and dissolving theforegoing allyl ether type cross-linking agent (b) or a polymerizationmethod, so-called a reversed phase suspension polymerization, forcarrying out polymerization of a similar aqueous monomer solution bydispersing and suspending the solution in an organic hydrophobic solventsuch as hexane, toluene, xylene and the like in the presence of adispersant makes it possible to produce a gel highly viscose for a longduration under high concentration alkaline conditions and to produce agel having extremely excellent drain property and a large particle size.

In this invention, common method may be employed for the polymerizationmethod of (meth)acrylic acid (alkali metal salts) by the aqueoussolution polymerization or the reversed phase suspension polymerizationand examples are a polymerization method using a radical polymerizationinitiator and methods by radiating radiation, ultraviolet rays, electronbeams, and the like.

In the method using a radical polymerization initiator, usable as theinitiator are azo compounds [azobisisovaleronitrile,azobisisobutyronitrile, 4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis[2-methyl-N-(2 -hydroxyethyl)propioneamide,2,2′-azobis(2-amidinopropane) hydrochloride and the like]; inorganicperoxides [hydrogen peroxide, potassium persulfate, ammonium persulfate,sodium persulfate, and the like]; organic peroxides[di-tert-butylperoxide, cumene hydroperoxide, and the like]; redoxinitiators [combination of reducer such as alkali metal sulfites orbisulfite, ammonium sulfite, ammonium hydrogen sulfite, L-ascorbic acidand the like with peroxide such as alkali metal persulfates, ammoniumpersulfate, hydrogen peroxide and the like]; and combination of two ormore of them.

The method for polymerization using the initiator is no particularlyrestricted and although it depends on the types of initiators to beused, the polymerization temperature is preferably −10° C. to 100° C.and further preferably −10° C. to 80° C. in order to increase thepolymerization degree of (meth)acrylic acid (alkali metal salts).

Also, it is not particularly restricted, the amount of the initiator ispreferably 0.000001 to 3.0% by weight and further preferably 0.000001 to0.5% by weight to the total weight of (meth)acrylic acid and/or theirmetal salts in order to increase the polymerization degree.

Regarding the polymerization concentration of the aqueous solutionpolymerization, although it is variously changed depending on otherpolymerization conditions, the polymerization concentration ispreferably 10 to 40% by weight and more preferably 10 to 30% by weightsince pseudo-cross-linking (self-cross-linking) of a monomer itselfeasily takes place in parallel to the polymerization reaction if thepolymerization concentration is increased to result in decrease of theabsorption amount and the average polymerization degree of straightchain polymers, difficulty in temperature control at the time ofpolymerization, decrease of the average polymerization degree ofpolymers and increase of oligomer components. Further, regarding thepolymerization temperature, it is preferable to be −10° C. to 100° C.and further preferably −10 to 80° C.

Regarding the dissolved oxygen amount at the time of polymerization,although it depends on the additional amount of the radical initiator,the amount is preferably 0 to 2 ppm and further preferably 0 to 0.5 ppm.

In the present invention, the neutralization degree of (meth)acrylicacid at the time of polymerization is not particularly restricted if aprescribed amount of the allyl ether type cross-linking agent (b) iscompletely dissolved in an aqueous monomer solution, however the allylether type cross-linking agent (b) is generally insufficient in thesolubility in water and especially its solubility in an aqueous solutionof alkali metal (meth)acrylates is extremely low, so that thecross-linking agent (b) sometimes becomes impossible to carry outprescribed cross-linking attributed to that the agent is sometimesisolated from the aqueous monomer solution to make it impossible tocarry out prescribed cross-linking even if the prescribed amount of theallyl ether type cross-linking agent (b) is added and hence theneutralization degree of the (meth)acrylic acid at the time ofpolymerization is preferably adjusted to be 0 to 30% by mole to carryout polymerization and further neutralization is carried out based onthe necessity after the polymerization and it is further preferable tocarry out polymerization in un-neutralized state and then to carry outneutralization after polymerization based on the necessity.

Further, if (meth)acrylic acid is polymerized in the same condition, thepolymerization degree is increased more in the case of lowerneutralization degree, it is therefore preferable to carry outpolymerization in the low neutralization state in order to increase thepolymerization degree of the polymers.

Regarding the reversed phase suspension polymerization, which is one ofpolymerization methods to be employed for the present invention, thepolymerization method is a method for carrying out polymerization bysuspending and dispersing an aqueous solution of (meth)acrylic acidand/or their alkali metal salts in a hydrophobic organic solventrepresented by hexane, toluene, xylene and the like in the presence of adispersant and also in the case of this polymerization method, themonomer concentration in the aqueous monomer solution is preferably 10to 40% by weight and further preferably 10 to 30% by weight, too.

Incidentally, regarding the reversed phase suspension polymerization, itis essential to use a dispersant at the time of polymerization andexamples of the dispersant are surfactants, e.g. sorbitan fatty acidesters, such as sorbitan monostearic acid ester with HLB of 3 to 8,glycerin fatty acid esters such as glycerin monostearic acid ester,sucrose fatty acid esters such as sucrose distearic acid ester; polymerdispersants (hydrophilic group; 0.1 to 20% by weight, the weight averagemolecular weight; 1,000 to 1,000,000) having hydrophilic groups in amolecule just like ethylene/acrylic acid copolymer, maleic-modifiedethylene/vinyl acetate copolymer, styrene sulfonic acid (Na)/styrenecopolymer and soluble in a solvent in which the aqueous monomer solutionis to be dispersed and since the suspended particle of the aqueousmonomer solution can be enlarged more in the solvent and awater-containing gel with a large particle diameter can be produced inthe case of using a polymer dispersant as a dispersant, it is preferableto use the polymer dispersant.

The additional amount of a surfactant and/or a polymer dispersant ispreferably 0.1 to 20% by weight and further preferably 0.5 to 10% byweight to a hydrophobic organic solvent.

The W/O ratio of an aqueous monomer solution and a hydrophobic organicsolvent in the reversed phase suspension polymerization is preferably0.1 to 2.0 and further preferably 0.3 to 1.0 on the basis of weight.

In the present invention, it is preferable to carry out polymerizationin the condition wherein the average weight polymerization degree ispreferably 5,000 to 1,000,000 and further preferably 10,000 to 1,000,000in the case of the foregoing mild polymerization of an aqueous solutionof (meth)acrylic acid (alkali metal salts) without using a cross-linkingagent. If the polymerization is carried out in the condition that theaverage polymerization degree becomes 5,000 or higher, using a properamount of a cross-linking agents makes it possible to lower theviscosity of an aqueous high concentration alkaline solution mixed witha gelating agent and/or to prevent increase of stringiness of thesolution. The above polymerization degree is measured by gel permeationchromatography method (GPC method).

Generally, methods applicable for polymerizing (meth)acrylic acid(alkali metal salts) include, other than the aqueous solutionpolymerization and the reversed phase suspension polymerization,so-called deposition (precipitation) polymerization method for carryingout polymerization an acrylic acid in a polar solvent such as anaromatic hydrocarbon and an alcohol and promoting polymerization basedon the difference of the solubility between the monomer and the polymerin the polar solvent, an emulsion polymerization method for carrying outpolymerization using an acrylic acid and/or its alkali metal salts usingan emulsifying agent, so-called bulk polymerization method for carryingout acrylic acid (alkali metal salts) using no solvent and the like.However, the polymer produced by the precipitation polymerization or theemulsion polymerization generally becomes finely granular and they areimpossible to provide an aiming polymer to be a gel with a largeparticle size necessary to prevent the precipitation of a zinc powder inan aqueous alkaline solution. Even if the particle diameter of a driedpolymer produced by the precipitation polymerization method or theemulsion polymerization method followed by granulation is enlarged, thestrength in the junction parts becomes weak and thus most of thegranulated polymer is broken down to a fine powder state as it is beforewhen it is mechanically stirred in an aqueous alkaline solution, so thatthese methods are not suitable for the method for producing the gel witha large particle size in an aqueous alkaline solution.

Further, in the precipitation polymerization, polymerization isgenerally carried out in a polar solvent such as aromatic hydrocarbons,alcohols and the like and these polar solvents have a high chaintransfer constant to the growing radicals of the monomer, so that theaverage polymerization degree of polymers polymerized in the solventstends to be lowered and oligomers are easy to be produced.

Regarding bulk polymerization, if the polymerization is carried out withapproximately 100% of the monomer concentration, an immense quantity ofpolymerization heat is generated to make polymerization temperaturecontrol extremely difficult and consequently it is made difficult toobtain a polymer with a high molecular weight and to produce a largeamount of oligomers. Further, also in precipitation polymerization, itis general to carry out polymerization in a polar solvent such asaromatic hydrocarbons and alcohols and these polar solvents have a highchain transfer constant to the growing radicals of the monomer, so thatthe average polymerization degree of polymers polymerized in thesolvents tends to be lowered and oligomers are easy to be produced.

Polymers containing a large amount of polymers with a loweredpolymerization degree of acrylic acid monomers and oligomers requireaddition of a large amount of a cross-linking agent in order to lowerthe stringiness by cross-linking un-cross-linked polymers, howeverindependently of the molecular weight of polymers, the absorption amountof the cross-linked polymer (A) in an aqueous high concentrationalkaline solution tends to be decreased in proportion to the additionalamount of the cross-linking agent, the decrease of the stringiness andthe increase of the viscosity of the aqueous alkaline solution becomeunbalance to make it difficult to produce the cross-linked polymerhaving the above described physical properties in the present invention.

Further, just like a bulk polymerization, if (meth)acrylic acid (alkalimetal salts) are polymerized in a high concentration, kind ofpseudo-cross-linking reaction, so-called self-cross-linking, is promotedin parallel to the polymerization owing to the characteristics of themonomers to make it extremely difficult to control the cross-linkingdegree and production of a desired gelating agent of the presentinvention becomes difficult.

As described above, the cross-linked polymer (A) obtained bypolymerization by the aqueous solution polymerization or the reversedphase suspension polymerization has the following properties.

(i) A gel with a large particle size and hardly broken even beingstirred in an aqueous alkaline solution can be produced. Consequently,using the polymer (A) as a gelating agent for an alkaline cell, a zincpowder cannot be precipitated through the gel with a large particlesize, so that the gelating agent can improve the discharge propertiesand the life of the cell. Further, since the zinc powder cannotpenetrate the gel with a large particle size, the practical zinc powderconcentration is increased and the contacting frequency of zinc powerparticles is increased and thus not only the discharge properties andthe life of the cell are improved but also the decrease of voltage andshort-circuitting current can be prevented even at the time of impactaffecting since the gel with a large particle size is hard to move.

(ii) Since polymerization can be carried out in controlledpolymerization temperature and under mild polymerization conditions andwater with a low chain transfer constant is used as a solvent, theaverage polymerization degree of a polymer can be increased and oligomercomponents can be decreased. Consequently, in the case of using thepolymer as a gelating agent for a cell, the polymer can be satisfactorysimultaneously in both of the viscosity increase and the stringinessdecrease of an aqueous high concentration alkali solution, so that thepolymer can be satisfactory simultaneously in both workabilityimprovement at the time of high speed loading of a cell with an alkalineelectrolytic solution owing to the low stringiness and cell propertyimprovement owing to the stabilization of a zinc powder attributed toincrease of the viscosity of the alkaline electrolytic solution.

In the present invention, the cross-linked polymer (A) is preferably across-linked polymer produced by cross-linking a polymer, which has theaverage polymerization degree of 5,000 to 1,000,000, comprises(meth)acrylic acid and/or their alkali metal salts as main constituentmonomers, is produced by an aqueous solution polymerization method or areversed phase suspension polymerization method, with an allyl ethertype cross-linking agent (b) having 2 to 10 allyl groups in a moleculeand the additional amount of the agent (b) is preferably 0.05 to 1.0% byweight [the cross-linked polymer (A′)] to the total weight of the(meth)acrylic acid and/or their alkaline metal salts.

In the present invention, a water-containing gel of the polymer ofobtained by the aqueous solution polymerization or the reversed phasesuspension polymerization is generally used being dried.

Regarding the drying method of the water-containing gel, in the case ofthe aqueous solution polymerization, the examples of the method can becarried out as follows: a water-containing polymer gel is segmented to acertain extent (the level of the segmentation is about 0.5 to 20 mmsquare) by a meat chopper type or cutter type coarse pulverizer or madeto be like a noodle and mixed with an alkali metal hydroxide based onnecessity to neutralize the water-containing gel, and then, theresulting water-containing gel is subjected to permeation drying (bylayering the water-containing gel on a punched metal or a screen andforcibly ventilating a hot wind at 50 to 150° C.) or to ventilationdrying (by putting a water-containing gel, drying the gel by ventilatingand circulating a hot wind, and further drying while segmenting the gelby a machine such as a rotary kiln. Between the methods, the permeationdrying is preferable to carry out efficient drying within a short time.

On the other hand, the drying method of a water-containing gel in thecase of the reversed phase suspension polymerization is generallycarried out by vacuum drying (the pressure decrease degree;approximately 100 to 50,000 Pa) or the foregoing ventilation dryingafter solid-liquid separation of the polymerized water-containing geland the organic solvent by decantation or the like.

As another drying method for a water-containing gel in the aqueoussolution polymerization, there disclosed in Japanese Patent No. 8-28216is a contact-drying method comprising steps of contracting and extendingthe water-containing gel on a drum drier and drying the gel, howeversince the water-containing gel is inferior in the thermal conductivity,a thin film of the water-containing gel has to be formed on the drum forthe drying. However, the material of a widely sold drum dry is generallyiron or a metal such as iron, chromium, nickel and the like with a lowerionization tendency than zinc and therefore the contacting frequencybetween the drum metal face and the water-containing gel is extremelyheightened and further the water-containing gel is a water-containinggel of poly(meth)acrylic acid and/or their alkali metal salts andtherefore the content of the metal ions dissolved in the gel isincreased. Further, since the contacting frequency between the foregoingwater-containing gel and the drum is extremely high and the foregoingwater-containing gel has high viscosity, it is required for the driedproduct to be peeled from the drum drier by bringing a knife-like toolinto contact with the drum drier and owing to the mechanical abrasion ofthe drum and the knife-like tool, the metal faces of the drum and theknife-like tool are worn out and the dried product is contaminated withthe metals. As described above, in the case the contact drying method isemployed using the drum drier, the gelating agent is easily becontaminated with metal ions and metal powders and if a gelating agentcontaining a rather large amount of ions and powders of these metalswith a lower ionization tendency than zinc (metals with a lower normalelectrode potential than zinc and including metals having atomic symbolsof Cr, Fe, Ni, Sn, Pb, Cu, Hg, Ag and the like) is used as the gelatingagent for an alkaline cell, cells are formed between the zinc powder andthe contaminating metal ions in the cell and hydrogen gas is evolved bythe electrolysis to increase the internal pressure of the cell and causeleakage of the alkaline solution and in some extreme cases, the cell isbroken and therefore the drying method is not preferable.

Further, the thin film-like dried product obtained by contracting andextending the water-containing gel on the drum drier and drying the gelis made to be a flaky particle even if the dried product is pulverizedthereafter and adjusted as to have a desired particle size, so that thestrength of the dried product is considerably inferior in the strengthas compared with that of a pulverized product of a block-like productdried by the permeation drying method or the ventilation drying methodand in the case the obtained powder is swollen in an aqueous alkalinesolution with a high concentration and then mechanically stirred andmixed with a zinc powder, the swollen gel is broken to be small and thusthe drying method is not preferable.

In the present invention, although it depends on the drier to beemployed and the drying duration, the drying temperature at the time ofdrying the water-containing gel is preferably 50 to 150° C. and furtherpreferably 80 to 130° C. If the drying temperature is 150° C. or higher,the polymer is sometimes cross-linked by the heat at the time of dryingto lower the absorption amount and the viscosity and on the other hand,if drying at 50° C. or lower, the drying takes a long time and is notefficient. Also, although it depends on the drier to be employed and thedrying temperature, the drying duration is preferably 5 to 300 minutesand further preferably 5 to 120 minutes.

The dried product of a cross-linked polymer obtained in such a manner ispulverized and powdered based on the necessity. A well-known method canbe employed for the pulverization method and pulverization can becarried out, for example, by an impact pulverizer (a pin mill, a cuttermill, a squirrel mill, an ACM pulverizer, and the like) and an airpulverizer (a jet pulverizer and the like).

Incidentally, in the case of pulverizing a dried product, it is notpreferable to use a pulverizer comprising rotation parts in which metalsare brought into direction contact with one another since the metalpowders generated by mechanical abrasion are possible to contaminate thegelating agent.

The dried powder based on the necessity may be subjected to a sievingapparatus (a vibration sieving apparatus, a centrifugal sievingapparatus and the like) equipped with a desired screen based on thenecessity to obtain a dried powder with a desired particle diameter.

Incidentally, in the present invention, in any stage after the drying,contaminating metal powders of such as iron may be removed using an ironremoving apparatus. However, even if iron removal is rather finelycarried out using the iron removing apparatus, it is difficult to removenon-magnetic metals by the iron removing apparatus and further evenmagnetic metals, those contained in the dried polymer particle andadhering to the dried particle cannot be removed and therefore it isdesirable to pay careful consideration to the production facilities soas to avoid contamination of these metals from the beginning.

Gelating Agent

In the present invention, although the particle size [the condition (1)]of the gelating agent to be used differs depending on the size of a cellfor which the gelating agent is used and the size of a zinc powder, theparticle size of the dried powder is generally so adjusted as to contain50% by weight or more of the gelating agent with the particle size ofpreferably 300 to 4000 μm and more preferably 500 to 2000 μm after thegelating agent is swollen and stirred in an aqueous solution of 40% byweight of potassium hydroxide. If the powder contains 50% by weight ormore of the swollen gelating agent with the average particle size of 300to 4000 μm, the precipitation of the zinc powder in the cell can beprevented and there takes place no problem at the time of injecting thegelating agent in the cell.

Regarding the particle size at the time of drying, although it dependson the magnification of the swelling of the gelating agent in an aqueousalkaline solution and the distraction degree of the gel in the case ofstirring the gel in the aqueous alkaline solution, the particle size ispreferably 100 to 1,000 μm and further preferably 200 to 900 μm sinceone side of each gelating agent particle is generally expanded about 3to 4 times by swelling when the gelating agent is stirred in the aqueousalkaline solution.

The stringiness [the condition (2)] of a gelating agent of the presentinvention is generally 0 to 20 mm and preferably 0 to 15 mm in the caseof an aqueous solution of 40% by weight of potassium hydroxideconcentration and containing 3% by weight of the gelating agent.

If the stringiness is 20 mm or lower, the drain property is excellent atthe time of high speed injection of the gelating agent-containingalkaline electrolytic solution to a cell and the electrolytic solutiondoes not adhere to the outside of the cell to prevent deterioration ofthe workability and unevenness of the injection amount of theelectrolytic solution per one cell is also narrowed and therefore it ispreferable for the stringiness to be within the range.

In the present invention, the method for producing a gelating agentsatisfying that the particle size [the condition (1)] and thestringiness [the condition (2)] of the swollen gel are both within therespective ranges is as described above and points of the method can besummarized as follows.

(i) An allyl ether type cross-linking agent (b) in a prescribed amount(within a range of 0.05 to 1.0% by weight, nevertheless, since theoptimum point of the cross-linking agent amount differs depending on theaverage polymerization degree of a polymer and adjustment within thedefined range is required.) is added to an aqueous monomer solutioncontaining mainly (meth)acrylic acid and/or their alkali metal salts andthe cross-linking agent is completely and evenly dissolved in theaqueous monomer solution.

(ii) A water-containing gel of the cross-linked polymer (A) is producedby carrying out polymerization by an aqueous solution polymerizationand/or a reversed phase suspension polymerization in mild polymerizationconditions wherein the average polymerization degree of a polymerbecomes 5,000 to 1,000,000 in the case of adding no cross-linking agent(b) and excess self-cross-linking (the polymerization concentration ispreferably 40% by weight or lower) hardly takes place.

(iii) In the case of the aqueous solution polymerization, after theobtained water-containing gel is segmented to a certain extent based onthe necessity, a hydroxide of alkali metals is added based on thenecessity to adjust the neutralization degree and drying is carried outby a permeation drying method or a ventilation drying method. In thecase of the reversed phase suspension polymerization, after thewater-containing gel is subjected to solid-liquid separation, drying iscarried out by a vacuum drying method or a ventilation drying method.

Incidentally, in order to suppressing the thermal cross-linking of thepolymer by heating even at the time of drying, the drying is carried outwithin a time as short as possible while the drying temperature (theproduct temperature) being controlled to be 150° C. or lower (preferably130° C. or lower).

(iv) The dried and pulverized product is pulverized based on thenecessity and sieved using a sieving apparatus based on the necessity toproduce a gelating agent mainly containing particles of its driedproduct with the particle size of 100 to 1,000 μm. Since one side ofeach gelating agent particle of the present invention is generallyexpanded about 3 to 4 times by swelling when the gelating agent isstirred in the aqueous alkaline solution, the main gelating agentparticle obtained has the particle size of 300 to 4000 μm in an aqueousalkaline solution.

(v) The neutralization is carried out within a defined extent of theneutralization degree.

Further, regarding the viscosity [the condition (3)] of a gelating agentof the present invention, the aqueous potassium hydroxide solution of40% by weight concentration containing 3% by weight of the gelatingagent has viscosity of 50 to 1,000 Pa.s, preferably 100 to 200 Pa.s at40° C. at the beginning and after sixty days. If the viscosity is 50Pa.s or higher, the precipitation of a zinc powder in a cell can almostcompletely be prevented and if it is 1,000 Pa.s or lower, the handlingproperty of the aqueous potassium hydroxide solution becomes relativelyeasy.

The methods described in the foregoing description (i) to (v) may beapplied for the method of producing the gelating agent in a manner thatthe viscosity [the condition (3)] of the aqueous potassium hydroxidesolution containing the gelating agent is within a prescribed range.

Further, regarding the content [the condition (4)] of a metal with alower ionization tendency than zinc in the gelating agent of the presentinvention, the content of the metal with a lower ionization tendencythan zinc in the gelating agent can be controlled to be within 0 to 15ppm and preferably 0 to 10 ppm by sufficiently paying consideration onthe raw materials to be used and the foregoing production facilities.

If the content of the metal with a lower ionization tendency than zincin the gelating agent is more than 15 ppm, although depending on the.structure and the capacity of a cell to be used and the additionalamount of a gelating agent to the cell, cells are formed between thezinc powder and the contaminating metal ions in the cell and hydrogengas is evolved by the electrolysis to increase the internal pressure ofthe cell and cause leakage of the alkaline solution and in some extremecases, the cell is broken and therefore it is not preferable.

A gelating agent of the present invention is preferable to contain 0 to30% by weight, preferably 0 to 20% by weight, of soluble components inthe aqueous solution when the gelating agent is dissolved in an aqueouspotassium hydroxide solution of 10% by weight concentration.

If the soluble components of the gelating agent is 30% by weight orlower, the stringiness of the aqueous alkaline solution can be improvedand the viscosity decrease can be prevented for a long duration.

In order to lower the content of the soluble components, the averagepolymerization degree of the polymer is increased or the amount of thecross-linking agent is increased, however if the cross-linking agent isincreased, it sometimes occurs that the absorption amount of thegelating agent is lowered and that the viscosity of the aqueous alkalinesolution mixed with the gelating agent is decreased and therefore, it isbetter to increase the average polymerization degree of the polymer.

The methods applicable for packing a gelating agent of the presentinvention in an alkaline cell are (I) a method carried out by previouslymixing the gelating agent of the present invention, an alkalineelectrolytic solution (for example, an aqueous potassium hydroxidesolution with a high concentration and containing zinc oxide based onthe necessity), and a zinc powder (and/or a zinc alloy powder) toproduce a mixture of an anode substance and filling an anode containerof the cell with the obtained mixture to form a gel-type anode and (II)a method carried out by filling a anode container of a cell with thegelating agent of the present invention and a zinc powder (and/or a zincalloy powder) and then filling the container further with an alkalineelectrolytic solution to produce a gel-type anode and the method (I) ispreferable since it is capable of evenly dispersing the zinc powder inthe anode container of the cell.

The additional amount of the gelating agent is preferably 0.5 to 10% byweight and further preferably 1.0 to 5.0% by weight to the alkalineelectrolytic solution although it variously differs depending on thestructure of the anode container, the particle diameter of the foregoingzinc powder, and the additional amount to the alkaline electrolyticsolution. If the additional amount is from 0.5 to 10% by weight, theviscosity of the alkaline electrolytic solution becomes proper and thezinc powder can be prevented from precipitation and the handlingproperty also becomes easy.

In the present invention, the method (I) may further comprises a step ofadding another gelating agent in combination based on the necessitywithin an extent in which no problem is caused on the workability andthe cell properties for the purpose to improve the fluidity of themixture of the anode substance at the time of filling.

As another gelating agent, examples are CMC, natural gum,poly(meth)acrylic acid and/or their alkali metal salts, finelycross-linked type poly(meth)acrylic acid and/or their salts, a finepowder of a gelating agent of the present invention, poly(vinyl alcohol)and the like. Among them, finely powder-state finely cross-linked typepoly(meth)acrylic acid and/or their salts and a fine powder of agelating agent of the present invention are preferable since the resinitself has relatively low stringiness and can provide the fluidity atthe time of filling with the anode substance mixture.

If the particle size of a thickener to be added based on the necessityhas the average particle diameter of 0.1 to 100 μm and furtherpreferably 0.1 to 50 μm as a dried product, the particle swollen in analkaline state is kept small even in the case stringiness of the anodesubstance mixture is slightly increased owing to the addition of anothergelating agent and the amount of the anode substance mixture used forfilling the cell is not so much affected and therefore it is preferable.

The additional amount of gelating agents to be added based on thenecessity is preferably 0 to 5.0% by weight and further preferably 0 to3.0% by weight to the alkaline electrolytic solution.

The addition method of another gelating agent may be any one of thefollowing methods: a method by previously dry blending a gelating agentof the present invention and another gelating agent and then blending azinc powder and other anode substances such as an alkaline electrolyticsolution with the obtained mixture; a method adding and mixing anothergelating agent at the time of producing the mixture of anode substancesdifferently from the gelating agent of the present invention, a methodby mixing the alkaline electrolytic solution with another gelating agentand then mixing the gelating agent of the present invention and a zincpowder and the like and any method as long as it can add a prescribedamount of another gelating agent based on the necessity can be employed.(Examples)

Hereinafter, the present invention will more particularly be describedaccording to examples and comparative examples, however the presentinvention is not at all restricted to these examples.

The measuring tests were carried out to measure the following (i) to(vi) by the following methods: (i) the absorption amount of the gelatingagent in an aqueous potassium hydroxide solution with 40% by weightconcentration; (ii) the particle size of the gel (the content of 300 to4000 μm, the content of 500 to 2000 μm); (iii) the stringiness; (iv) theviscosity of the aqueous potassium hydroxide solution with 40% by weightconcentration after 1 day and 60 days; (v) the content of the metal withthe lower ionization tendency than zinc in the gelating agent; and (vi)the soluble component amount in an aqueous potassium hydroxide solutionwith 10% concentration. Hereinafter, % shows % by weight unless aspecific definition is given.

(i) the absorption amount of the gelating agent in an aqueous potassiumhydroxide solution with 40% concentration:

A gelating agent in 2.0 g was put in a bag made of a nylon screen with250 meshes and having an opening in one side and immersed in an aqueouspotassium hydroxide solution with 40% concentration (super gradereagent) for 3 hours and then the nylon screen was pulled up to carryout draining for 30 minutes and the same operation was carried out usingan empty nylon screen bag. The absorption amount was measured based onthe following equation:

 absorption amount (g/g)=(the weight of the nylon screen afterimmersion−the weight of the nylon screen of the blank test)/2

(ii) the particle size of a gel after the gel was stirred in an aqueouspotassium hydroxide solution with 40% concentration:

Together with a rotator (with 4 cm length), 2.0 g of a gelating agentand 300 g of an aqueous potassium hydroxide solution with 40%concentration were put in a 500 ml poly beaker and stirred at 600 rpmspeed at a room temperature by a magnetic stirrer. The alkaline solutionafter the stirring was poured on a sieve with 20 cm diameter equippedwith JIS 50 meshes (screen mesh opening: 300 μm) in the lower stage andJIS 4.7 meshes (screen mesh opening: 4,000 μm) and washed with anaqueous potassium hydroxide solution with 40% concentration severaltimes. After 30 minute-draining was carried out, the excess aqueouspotassium hydroxide solution adhering to the screen was wiped by a Kimwipe and the weight of the gel remaining on the upper part of the sievewith 50 meshes was measured and based on the following equation, thecontent (%) of the gel with 300 to 4,000 μm size in the potassiumhydroxide was measured:

the content (%) of the gel with 300 to 4,000 μm size=100×[the weight (g)of the gel on 50 meshes]/[2×absorption amount (g) of the gelatingagent].

The same operation was carried out using JIS 30 meshes (screen meshopening: 500 μm) in the lower stage and JIS 8.6 meshes (screen meshopening: 2,000 μm) to measure the content (%) of the gel in the aqueouspotassium hydroxide solution.

the content (%) of the gel with 500 to 2,000 μm size=100×[the weight (g)of the gel on 30 meshes]/[2×absorption amount (g) of the gelatingagent].

(iii) the stringiness of an aqueous potassium hydroxide solution with40% concentration containing 3% of a gelating agent:

A rotatable elliptical glass ball with 11 mm length and 8 mm width andequipped with a cylindrical joining part with 2.5 mm diameter and 10 mmlength attached to one side of a stringiness tester (Kyowa ChemicalIndustry Co., Ltd.) was immersed in a gel sample of a gelating agentwhose viscosity after 1 day was measured to the root part of thecylindrical joining part and the glass ball was elevated at 16 mm/secondto be pulled out the gel.

At the time when the glass ball was completely separated from the gelsample, the elevation of the glass ball was stopped and using ameasuring apparatus attached to the stringiness tester, the distance(mm) of the point where the glass ball was parted from the gel from theupper face of the gel was measured. The similar operation was repeatedin total 10 times and the average value was defined as the stringiness(mm).

(iv) the viscosity of the aqueous potassium hydroxide solution with 40%concentration containing 3% of a gelating agent:

An aqueous potassium hydroxide solution with 40% concentration in 200 gwas put in a 250 ml transparent polymer container equipped with a coverand while the content being stirred as to prevent undissolved lumpformation, 6.0 g of a gelating agent was added little by little. Afterthe even gelling took place entirely (or the viscosity was increased),the container was put in a thermostat at 40° C. and left for 1 day whilebeing kept closed and then the viscosity of the content was measured bya digital B type viscometer (manufactured by TOKIMEC Co. Ltd.) and themeasured viscosity was defined as the viscosity after 1 day (measurementtemperature: 40° C., rotor No.4 rotation speed: 3 rpm).

Some of the sample whose viscosity measurement was finished was closedand again put in the thermostat at 40° C. and left for 60 days whilebeing closed and then the viscosity of the content was measured in thesimilar conditions using the digital B-type viscometer and defined asthe viscosity after 60 days.

(v) the content of the metal with the lower ionization tendency thanzinc: To an evaporating dish of platinum, 3 g of a gelating agent and 4ml ion-exchanged water were put and gelling was carried out. The gelsample was mixed with 6 ml of concentrated sulfuric acid and incineratedby heating under the platinum dish by a burner and further heated for 5hours in an electric furnace (at 800° C.) to be completely incinerated.

A small amount of pure water was poured several times to the platinumdish to wash out the content and transfer the content to a 20 ml messflask and the volume was adjusted to be 20 ml in total and the contentsof metals of Fe, Ni, Cr, Sn, Pb, Cu, and Ag were measured by an ICP(inductively coupling plasma) method. Separately, calibration curves ofthe foregoing metals were produced using standardized solutions and thecontents of the respective metals were measured using the calibrationcurves:

the metal ion content (ppm)=total amount (g) of Fe, Ni, Cr, Sn, Pb, Cu,and Ag in the gelating agent/the gelating agent sample amount (g).

(vi) the soluble component amount in an aqueous potassium hydroxidesolution with 10% concentration:

To a 500 ml beaker, 1 g of a gelating agent and 200 g of an aqueouspotassium hydroxide solution with 10% concentration were poured andstirred at 300 rpm for 3 hours using a magnetic stirrer. The stirredsolution was filtered with a filtration paper (No. 2 type produced byToyo Filter Paper Co., Ltd.) to recover the filtrate. The resultingfiltrate in 20 g was mixed with 30 g of ion-exchanged water and furtherwith an aqueous 10% sulfuric acid solution to adjust the pH at 7.0 andobtain a sample solution. As a blank, 30 g of ion-exchanged water wasadded to 20 g of the used aqueous potassium hydroxide solution with 10%concentration and the aqueous 10% sulfuric acid solution was added toadjust the pH at 7.0 and obtain a blank solution.

Using an automatic titration apparatus (GT-05 type manufactured byMitsubishi Chemical Co. Ltd.), a 0.01 N aqueous potassium hydroxidesolutions added to the sample solution until the pH of the samplesolution was adjusted to be 10.0 once and further the 0.01 N aqueoushydrochloric acid solution was added until the pH of the sample solutionwas adjusted to be 2.7 and the amount ml (Va) of the 0.01 N aqueoushydrochloric solution required to adjust the pH at the value wasmeasured. The similar operation was carried out for the blank solutionand the additional amount ml (Vb) of the aqueous hydrochloric acidsolution was measured.

Based on the following equations 1, 2, 3, the soluble component amount(%) of a gelating agent in an aqueous potassium hydroxide solution wascalculated.

 M=(Va−Vb)×N  Equation-1

M: the potassium acrylate amount (mmol) in the sample solution, N: thenormality of the aqueous hydrochloric acid solution

W=M×E×D  Equation-2

W: the potassium acrylate weight in the sample solution, E: molecularweight of potassium acrylate, D: dilution ratio (200/20)

the soluble component amount (%)=W (g)×100/sample weight (g)  Equation-3

Incidentally, in the case the gelating agent composition containsmethacrylic acid, the foregoing E value was adjusted to be the molecularweight of potassium methacrylate. Regarding the polymers obtained bycopolymerization of monomers other than (meth)acrylic acid, thecarboxylic acid amounts per unit molecular weight were measured andcorrection was performed.

EXAMPLE 1

To a 2 liter beaker, 200 g of acrylic acid, 0.6 g of pentaerythritoltriallyl ether (0.3%/acrylic acid) (produced by Daiso Co., Ltd.), and800 g of ion-exchanged water were added and cooled to 8° C.

The resulting aqueous acrylic acid solution was put in a 1.5 liter heatinsulating polymerization tank and while nitrogen gas being introducedinto the aqueous solution to lower the dissolved oxygen amount of theaqueous solution to 0.1 ppm or lower and 4.0 g of an aqueous 0.1%hydrogen peroxide and 4.0 g of an aqueous 0.1% L-ascorbic acid solutionand 1.0 g of a 10% aqueous solution of 2,2′-azobis(2-amidinopropane)hydrochloride (trade name: V-50 produced by Wako Pure ChemicalIndustries, Ltd.) were added to the aqueous solution and the nitrogenpurge for the aqueous solution was continued until the polymerizationwas started. Since the polymerization was started and the viscosity ofthe aqueous acrylic acid solution was started increasing, the purge withnitrogen was stopped and polymerization was carried out for 6 hours. Thetemperature of the aqueous acrylic acid solution was measured by amulti-point thermometer and found that the highest temperature was 63°C.

Incidentally, in said polymerization, the average polymerization degreeof the polymer obtained by polymerization without using thepentaerythritol triallyl ether as a cross-linking agent was measuredusing GPC and found to be about 28,000.

The resulting block-type cross-linked water-containing gel was taken outfrom the heat insulating polymerization tank and the gel was segmentedto be 3 to 10 mm using a small type meat chopper (manufactured by LoyalCo. Ltd.) and then mixed with 222 g of an aqueous solution of 40% ofsodium hydroxide (super grade reagent) (neutralization degree 80% bymole) to be neutralized.

The neutralized water-containing gel was layered in 5 cm thickness on ascreen made of SUS with 850 μm opening and hot wind air at 120° C. wastransmitted through the water-containing gel for 1 hour using a smalltype permeation drier (manufactured by Inoue Metal Co., Ltd.) to dry thewater-containing gel.

The dried product was pulverized using a cooking mixer and particleswith particle diameter of 210 to 850 μm (JIS: 70 meshes to JIS:

18 meshes) were taken using sieves and thus obtain a gelating agent (1)of the present invention.

Regarding the gelating agent (1) of the present invention, the followingwere measured: the content of the metals in the gelating agent; theabsorption amount of the gelating agent in an aqueous potassiumhydroxide solution with 40% by weight concentration; the viscosity, thestringiness, and the particle size of the gel (the content of 300 to4000 μm, the content of 500 to 2000 μm) of the aqueous potassiumhydroxide solution with 40% by weight concentration and mixed with thegelating agent after 1 day and 60 days; and the soluble component amountin an aqueous potassium hydroxide solution with 10% concentration.

Further, the similar measurement was carried out for the examples 2 to 5and the comparative examples 1 to 10 and the results were shown in Table1.

EXAMPLE 2

A gelating agent (2) of the present invention was obtained by carryingout the similar operation as that of the example 1, except that theadditional amount of pentaerythritol triallyl ether was changed to be0.2 g (0.1%/acrylic acid) in the example 1.

EXAMPLE 3

A solution was obtained by mixing 0.1 g of ethylene glycol diglycidylether (Denalcol 810 produced by Nagase Chemicals Ltd.), 7.9 g ofmethanol, 2.0 g of ion-exchanged water and sufficiently mixed with 100 gof the gelating agent (2) obtained in the example 2 in the presentinvention. The mixed powder was put in an air circulation type drier at130° C. and heated for 30 minute to carry out surface cross-linking ofthe gelating agent and to obtain a gelating agent (3) of the presentinvention.

EXAMPLE 4

In a 1 liter beaker, 100 g of acrylic acid, 272.2 g of ion exchangedwater and 0.2 g of pentaerythritol triallyl ether (0.2%/acrylic acid)were mixed to dissolve the cross-linking agent. While the beaker beingcooling in ice bath, 27.8 g of an aqueous sodium hydroxide solution with40% concentration was added to neutralize some (20% by mole) of theacrylic acid. After the neutralized monomer solution was cooled to 5°C., 0.2 g of potassium persulfate was added as a polymerizationinitiator.

Using hot bath, 1000 ml of cyclohexane and 10 g of sodiumstyrenesulfonate/styrene block copolymer as a dispersant were mixed in 2liter separable flask equipped with a stirring apparatus and a condenser(a cooling apparatus) and the content was heated at 60° C. to dissolvethe dispersant in cyclohexane.

Nitrogen gas was introduced into the cyclohexane solution in theseparable flask to lower the dissolved oxygen in the cyclohexane andthen while the cyclohexane being stirred using the stirring apparatus,400 g of said aqueous monomer solution was dropwise added using atitration funnel and reversed phase suspension polymerization wascarried out at 60° C. polymerization temperature, and further oncompletion of the titration of the aqueous monomer solution, 2-hourheating was further performed to complete the suspension polymerizationand to obtain spherical water-containing gel with a large particle sizein cyclohexane.

After the rotation of the stirring apparatus was stopped and theproduced water-containing gel was precipitated, cyclohexane was removedby decantation and the remaining water-containing gel was washed withcyclohexane several times to remove the dispersant adhering to thewater-containing gel.

The obtained spherical water-containing gel with a large particle sizewas spread on a peeling paper and dried for 2 hours by a vacuum drier at80° C. (10,000 to 20,000 Pa). The particle size of the dried product wasmeasured to find that 92% of the product had 210 to 850 μm particle sizeand therefore the obtained product was used as it is as a gelating agent(4) of the present invention.

EXAMPLE 5

A gelating agent (5) of the present invention was obtained by blending75g of the gelating agent obtained by the example 1 of the presentinvention and 25 g of a finely cross-linking type polyacrylic acid finepowder (trade name: CARBOPOL 941 produced by BF Gridrich Company) inpowder state.

Regarding the gelating agent (5) of the present invention, the followingwere measured: the content of the metals in the gelating agent; theabsorption amount of the gelating agent in an aqueous potassiumhydroxide solution with 40% by weight concentration; the viscosity, thestringiness, and the particle size of the gel (the content of 300 to4000 μm, the content of 500 to 2000 μm) of the aqueous potassiumhydroxide solution with 40% by weight concentration and mixed with thegelating agent after 1 day and 60 days; and the soluble component amountin an aqueous potassium hydroxide solution with 10% concentration. Theresults were shown in Table 1.

Comparative Example 1

A commercialized carboxymethyl cellulose (CMC 2450 produced by DaicelChem. Ind., Ltd.) was used as a comparative gelating agent (I).

Comparative Example 2

A commercialized finely cross-linked polyacrylic acid fine powder(CARBOPOL 941 with the average particle size of about 20 μm produced byBF Gridrich Company) was used as a comparative gelating agent (II).

Comparative Example 3

A commercialized finely cross-linked polyacrylic acid fine powder(Junlon PW-150 with the average particle size of about 20 t m producedby Nihon Junyaku Co., Ltd.) in 20 g was mixed with an aqueous methanolsolution (a mixture of methanol/water=70/30) and granulated. Thegranulated product was dried at 100° C. by an air circulation type drierand then lightly pulverized with a cooking mixer and sieved using asieving apparatus to obtain the particles with 210 to 850 μm and theparticles were used as a comparative gelating agent (III).

Comparative Example 4

The gelating agent (1) obtained by the example 1 was pulverized using ajet mill pulverizer (manufactured by Nippon Neumatic Co. Ltd.) to makethe average particle size 20 μm.

The finely pulverized fine powder in 20 g was mixed with 10 g of anaqueous methanol solution (a mixture of methanol/water=70/30) andgranulated. The granulated product was dried at 100° C. by an aircirculation type drier and then lightly pulverized with a cooking mixerand sieved using a sieving apparatus to obtain the particles with 210 to850 μm and the particles were used as a comparative gelating agent (IV).

Comparative Example 5

To a 1.5 liter polymer beaker, 30 g of acrylic acid, 770 g of a 35%aqueous sodium acrylate solution, 2 g of ion exchanged water, 0.005 g(0.0017%/acrylic acid) of methylenebisacrylamide, 0.01 g(0.0034%/acrylic acid) of trimethylolpropane diallyl ether were addedand cooled to 10° C. using an ice bath. After nitrogen gas wasintroduced into the solution to lower the dissolved oxygen, 5 ml of anaqueous ammonium persulfate solution with 0.2% of ammonium persulfateand 5 ml of an aqueous SORBIT N solution with 0.06% concentration (apolymerization initiator and an ascorbic acid type reducing agent) wereadded and mixed to start the polymerization. The polymerization wascompleted in about 2 hours and the highest temperature reached about 85°C.

The water-containing gel after the polymerization was taken out from thepolymer container and segmented into 1 cm square using scissors. Thesegmented gel in about 10 g was put in 100 g of an aqueous methanolsolution with 60% concentration (a mixture of methanol/water=60/40) andimmersed in the aqueous methanol solution for 24 hours. When thewater-containing gel after immersion was observed, the surface of thewater-containing gel becomes opaque owing to discharge of water in thewater-containing gel, whereas the inside was as the water-containing gelas it was before the immersion and without regard to that, the gel wasput in an air circulation type drier at 105° C. and dried for 24 hours.

The dried product was pulverized using a cooking mixer and particleswith 210 to 850 μm were collected using a sieving apparatus and employedas a comparative gelating agent (V).

Comparative Example 6

94 g of sodium acrylate, 28 g of acrylic acid, 0.5 g ofN,N-methylenebisacrylamide, and 400 g of water were put in an openabletightly closed container and in nitrogen atmosphere, the solutiontemperature was kept at 20° C. and 1 g of an aqueous ammonium persulfatesolution with 0.5% of ammonium persulfate and 1 g of 0.5% sodiumhydrogen sulfite were added and mixed to start the polymerization. Thehighest temperature reached about 75° C.

After 6 hours, the water-containing gel was taken out from the tightlyclosed container and segmented into 0.5 to 2 mm by passing the gelthrough a meat chopper several times in order to carry out drying by adrum drier. The segmented water-containing gel was put between the drumdrier (produced by Kusunoki Machinery Co. Ltd.) made of an iron-chromiumalloy and heated at 160° C. and pressurizing rolls installed in the drumdrier and made of Teflon (the clearance of 0.5 mm) and thewater-containing gel was rolled in 0.5 mm film thickness on the drumdrier and dried for 3 minutes. After drying, a knife (made of a SUS)installed in the drum drier was brought into contact with the drum drierand the dried film was peeled from the drum drier. The thickness of thefilm was measured by a film thickness meter to find the thickness about0.2 mm.

The dried film was segmented by a cooking mixer and particles with 210to 850 μm were collected using a sieving apparatus and employed as acomparative gelating agent (VI).

Comparative Example 7

100 g of acrylic acid, 0.5 g of tetraallyloxyethane, and 400 g of waterwere put in an openable tightly closed container and in nitrogenatmosphere, the solution temperature was kept at 10° C. and 1 g of anaqueous hydrogen peroxide with 1% and 1 g of a 0.5% aqueous L-ascorbicacid solution were added and mixed to start the polymerization. Thehighest temperature reached about 65° C.

After 6 hours, the water-containing gel was taken out from the tightlyclosed container and segmented into 0.5 to 2 mm by passing the gelthrough a meat chopper several times in order to carry out drying by adrum drier. The segmented water-containing gel was put between the drumdrier made of an iron-chromium alloy and heated at 160° C. andpressurizing rolls installed in the drum drier and made of Teflon (theclearance of 0.5 mm) and the water-containing gel was rolled in 0.5 mmfilm thickness on the drum drier and dried for 3 minutes. After drying,a knife (made of a SUS) installed in the drum drier was brought intocontact with the drum drier and the dried film was peeled from the drumdrier. The thickness of the film was measured by a film thickness meterto find the thickness about 0.2 mm. The dried film was segmented by acooking mixer and particles with 210 to 850 μm were collected using asieving apparatus and employed as a comparative gelating agent (VII).

Comparative Example 8

A comparative gelating agent (VIII) was obtained by carrying out thesame operation as that of the example 1, except that the additionalamount of the pentaerythritol triallyl ether used in the example 1 waschanged to be 0.06 g (0.03%/acrylic acid).

Comparative Example 9

A comparative gelating agent (IX) was obtained by carrying out thesimilar operation to that of the example 1, except that the additionalamount of the polymerization initiators (hydrogen peroxide, ascorbicacid V-50) used in the example 1 was increased as much as 10 times and a20% aqueous ethanol solution (ethanol/water=20/80) was used in place ofion-exchanged water.

Incidentally, the average polymerization degree of the polymerizedpolymer without using the pentaerythritol triallyl ether, which was across-linking agent, was measured by GPC and found that the averagepolymerization degree was about 1,700.

Comparative Example 10

A commercialized water-absorptive resin (Junlon QP with the averageparticle size of about 100 μm produced by Nihon Junyaku Co., Ltd.) wasemployed as a comparative gelating agent (X).

Using the gelating agents (1) to (5) produced by the examples 1 to 5 andthe gelating agents (I) to (X) produced by the comparative examples 1 to10 and an alkaline electrolytic solution, the following properties weremeasured by the following methods: the precipitation property of a zincpowder [trade name: 004F (2)/68 produced by UNION MINIERES. A.), theinjection time, the unevenness of the injection amount, the hydrogen gasevolution amount, the retention duration and the impact resistance ofmodel cells. The results were shown in Table 2.

Precipitation of a Zinc Powder

To a 1 liter biaxial kneader (trade name: PNV-1 manufactured by IrieShokai Co., Ltd.), 500 g of an aqueous potassium hydroxide solution with40% concentration and 15 g of a gelating agent were added and mixed at50 rpm speed for 60 minutes to produce a gel-state aqueous potassiumhydroxide solution.

Then, 50 g of the produced gel-state aqueous potassium hydroxidesolution was put in a tightly closable sample vial with 50 ml ofcapacity (the diameter of 34 mm, the height of 77 mm, and made of apolypropylene) and foams entrained at the time of mixing was defoamed indecreased pressure and after that, 10 g of a zinc powder with theaverage particle size of 150 μm was added as evenly as possible to thegel-state aqueous potassium hydroxide solution.

The sample vial was tightly closed and kept at 40° C. in a thermostatfor 30 days and using an apparatus installed in a powder tester(manufactured by Hosokawa Micron Co., Ltd.), a screw pipe was tapped (30times/min) from 3 cm 300 times to promote the precipitation of the zincpowder. On completion of the tapping, the remotest distance (mm) of thezinc powder from the initial position of the zinc powder was measuredand the value was defined as the precipitation property (mm) of the zincpowder. [the injection duration and unevenness of the injection amount]

To a 1 liter biaxial kneader, 500 g of an aqueous potassium hydroxidesolution with 40% concentration and 15 g of a gelating agent were addedand mixed at 50 rpm speed for 60 minutes to produce a gel-state aqueouspotassium hydroxide solution. The produced gel-state aqueous potassiumhydroxide solution was transferred to a beaker and the foams entrainedat the time of mixing were defoamed in the decreased pressure.

The defoamed gel-state aqueous potassium hydroxide solution was suckedin the inside of a 20 ml injector having an injection inlet with theinner diameter of 5 mm and gauges of 0.1 ml unit.

The injector was compressed to 2.0 ml through the opening of the 5 mlsample vial (the inner diameter of 18 mm and the height of 40 mm) in theheight direction to inject the gel-state aqueous potassium hydroxidesolution and the duration (second) from the moment of the completion ofthe compression of the injector to the moment when the gel-state aqueouspotassium hydroxide solution was completely separated from the injectioninlet of the injector was measured by a stop watch. The similaroperation was repeated 20 times in total and the average value wasemployed as the injection duration (second).

The weight of the aqueous potassium hydroxide solution injected to thesample vial was measured (20 times) and the standard deviation (σ) ofthe injection amounts was calculated and employed as the unevenness ofthe injection amounts.

Hydrogen Gas Evolution Amount

To a 50 ml sample vial (the diameter of 34 mm, the height of 77 mm, andmade of a polypropylene), 15 g of a zinc powder (a reagent, the particlesize of about 50 μm), 50 g of an aqueous potassium hydroxide solutionwith 40% concentration saturated with zinc oxide, and 1.5 g of agelating agent were added and evenly mixed using a rod made of Teflon.

A cover (having a hole with the diameter of about 3 mm to make insertionof a gas detection tube possible to be inserted through and closed witha sealing tape) was put on the sample vial to close the inside and thesample vial was put in a thermostat at 50° C. for 10 days.

The sample vial was taken out after 30 days and a hydrogen gas detectiontube (Kitagawa-type gas detection tube, manufactured Komei RikagakuIndustry Co. Ltd., the hydrogen gas measurement range: 500 to 8000 ppm)was inserted into the vapor phase part of the sample vial through thepreviously opened hole of the cover to measure the hydrogen gasconcentration in the vapor phase.

Retention Duration of a Cell

To a 1 liter biaxial kneader, 500 g of an aqueous potassium hydroxidesolution with 40% concentration saturated with zinc oxide, 500 g of azinc powder, and 12.5 g of a gelating agent were added and mixed at 70rpm speed for 60 minutes to produce a gel-state aqueous zincelectrolytic solution.

Defoaming was performed in the decreased pressure and 15 g of the zincelectrolytic solution was injected in the inside of an anode containerof an LR-20 type model cell as shown in FIG. 1 to produce a model cell.

An external resistance of 2Ω at a room temperature (20 to 25° C.) wasconnected with the produced model cell and continuous discharge wascarried out and the duration to the time when the voltage was decreasedto 0.9 V was defined as the retention duration (hour). Similar operationwas carried out for the model cell kept at 50° C. in a thermostat for 60days after production of the model cell and the retention duration ofthe cell was measured.

Impact Resistance of a Cell

A model cell was produced in the same manner as described above andwhile continuous discharge being carried out by connecting an externalresistance of 2Ω at a room temperature (20 to 25° C.), the model cellwas dropped from the height of 1 m successively 10 times and the voltagevalues before the dropping and immediately after dropping were measuredand the impact resistance (%) was calculated according to the followingequation:

impact resistance (%)=(the voltage (V) immediately after dropping (10thtime)/the voltage (V) before dropping)×100.

Similar operation was carried out for the model cell kept at 50° C. in athermostat for 60 days after production of the model cell and the impactresistance of the cell was measured.

TABLE 1 Water-containing gel Soluble Absorption particle diameter (%)Viscosity (Pa.s) Metal component Gelating amount 300/4000 500/2000Stringiness After After 60 content amount agent (g/g) (μm) (μm) (mm) 1day days (ppm) (%) Example 1 Gelating 35 92 90 6.0 80 100 1.7 8 agent(1) Example 2 Gelating 40 83 81 12.0 110 120 1.8 16 agent (2) Example 3Gelating 40 83 80 11.8 110 120 1.8 16 agent (3) Example 4 Gelating 36 8785 8.0 60 80 0.8 12 agent (4) Example 5 Gelating 27 63 60 18.0 110 1202.0 25 agent (5) Comparative Gelating 32 0 0 38.2 80 8 7.6 — Example 1agent (I) (dissolved) Comparative Gelating 35 1 1 54.2 130 140 3.1 70Example 2 agent (II) (dissolved) Comparative Gelating 38 15 8 50.2 100110 4.3 72 Example 3 agent (III) (dissolved) Comparative Gelating 36 3 310.0 65 80 2.8 9 Example 4 agent (IV) Comparative Gelating 37 48 42 38.642 45 1.8 40 Example 5 agent (V) Comparative Gelating 35 7 5 67.6 40 3052.6 90 Example 6 agent (VI) (dissolved) Comparative Gelating 32 43 255.1 50 65 53.3 7 Example 7 agent (VII) Comparative Gelating 42 60 4637.5 100 120 1.7 32 Example 8 agent (VIII) Comparative Gelating 27 62 4636.2 25 30 1.8 41 Example 9 agent (IX) Comparative Gelating 38 35 2040.1 65 35 5.3 36 Example 10 agent (X)

TABLE 2 Retention duration Injection Hydrogen of a cell (hour) ImpactPrecipitation Injection amount gas Immediately After resistance Gelatingproperty of duration uneven- amount after 60-day- of a cell agent zinc(mm) (SEC.) ness (σ) (ppm) production storage (%) Example 1 Gelating 10.1 0.02 500> 15.2 15.1 97 agent (1) Example 2 Gelating 1 0.2 0.03 500>15.0 14.8 96 agent (2) Example 3 Gelating 1 0.2 0.03 500> 15.1 14.8 96agent (3) Example 4 Gelating 2.5 0.2 0.03 500> 14.8 14.7 95 agent (4)Example 5 Gelating 2.5 0.8 0.04 500> 14.0 13.8 90 agent (5) ComparativeGelating 55 3.8 0.21 500> 6.5 3.0 15 Example 1 agent (I) ComparativeGelating 48 4.0 0.15 500> 8.7 7.0 35 Example 2 agent (II) ComparativeGelating 46 3.8 0.20 500> 9.5 8.0 38 Example 3 agent (III) ComparativeGelating 30 1.2 0.04 500> 11.6 10.5 50 Example 4 agent (IV) ComparativeGelating 18.8 2.8 0.32 500> 12.8 11.0 65 Example 5 agent (V) ComparativeGelating 48 4.6 0.23 2100  9.4 5.6 30 Example 6 agent (VI) ComparativeGelating 13 0.3 0.05 2200  12.3 12.0 60 Example 7 agent (VII)Comparative Gelating 9 2.8 0.31 500> 13.0 12.5 70 Example 8 agent (VIII)Comparative Gelating 16 2.6 0.25 500> 10.2 9.0 40 Example 9 agent (IX)Comparative Gelating 13 2.4 0.30 500> 12.8 11.3 75 Example 10 agent (X)

A gelating agent of the present invention has the following effects.

(i) In the case of using a gelating agent of the present invention foran alkaline cell, a cell with durable discharge time and remarkablyexcellent impact resistance for a long duration can be produced.

(ii) Since an alkaline electrolytic solution containing a gelating agentof the present invention has good draining property, the solution cansufficiently satisfy the high speed charging with the alkalineelectrolytic solution required attributed to the recent tendency ofincreasing the speed of the cell production.

(iii) Since the unevenness of the charging amount per one cell with anelectrolytic solution is scarce in the case of charging, cells withuniform quality can be produced even by mass production.

(iv) Since hydrogen gas is scarcely evolved even if a zinc powder isbrought into contact in an alkaline electrolytic solution, there is noprobability of leakage of the electrolytic solution and damage of thecell owing to the increase of the inner pressure of the cell.

Industrial Applicability

Owing to the above described effects, a gelating agent of the presentinvention is useful as a gelating agent for not only a cylindricalalkaline cell but also a primary and a secondary alkaline cells such asan alkaline button battery, a silver oxide battery, a nickel-cadmiumstorage battery, a nickel-hydrogen storage battery and the like.

What is claimed is:
 1. A swelling-in-water type gelating agent of across-linked polymer (A) comprising (meth)acrylic acid and/or its alkalimetal salt as a main constituent monomer unit and obtained by an aqueoussolution polymerization or a reversed phase suspension polymerization,wherein the gelating agent is for an alkaline cell and satisfies thefollowing required conditions (1) to (4): required condition (1); thatthe gelating agent contains 50% by weight or more of a particle whoseswollen particle size becomes 300 to 4,000 μm when the gelating agent isswollen in an aqueous potassium hydroxide solution of 40% by weightconcentration; required condition (2); that the aqueous potassiumhydroxide solution of 40% by weight concentration containing 3% byweight of the gelating agent has 0 to 20 mm stringiness; requiredcondition (3); that the aqueous potassium hydroxide solution of 40% byweight concentration containing 3% by weight of the gelating agent hasviscosity of 50 to 1,000 Pa.s at 40° C. after one day and sixty days;and required condition (4); that the gelating agent contains 0 to 15 ppmof a metal with a lower ionization tendency than zinc.
 2. The gelatingagent for an alkaline cell according to claim 1, wherein the polymer (A)is a cross-linked polymer with 5,000 to 1,000,000 average polymerizationdegree and cross-linked by an allyl ether type cross-linking agent (b)having 2 to 10 of allyl groups in a molecule and the cross-linking agent(b) is added in 0.05 to 1.0% by weight to the total weight of the(meth)acrylic acid and/or its alkali metal salt and the gelating agentsatisfies the following required conditions (1) to (3): requiredcondition (1); that the gelating agent contains 50% by weight or more ofa particle whose swollen particle size becomes 300 to 4,000 μm when thegelating agent is swollen in an aqueous potassium hydroxide solution of40% by weight concentration; required condition (2); that the aqueouspotassium hydroxide solution of 40% by weight concentration containing3% by weight of the gelating agent has 0 to 20 mm stringiness; andrequired condition (3); that the aqueous potassium hydroxide solution of40% by weight concentration containing 3% by weight of the gelatingagent has viscosity of 50 to 1,000 Pa.s at 40° C. after one day andsixty days.
 3. The gelating agent for an alkaline cell according toclaim 2, wherein the gelating agent satisfies the following requiredcondition (4): required condition (4); that the gelating agent contains0 to 15 ppm of a metal with a lower ionization tendency than zinc. 4.The gelating agent for an alkaline cell according to claim 2, whereinthe agent (b) has 3 to 10 of allyl groups in a molecule and 1 to 5 ofhydroxyl groups in a molecule.
 5. The gelating agent for an alkalinecell according to claim 2, wherein the swollen particle satisfying therequired condition (1) has particle size of 500 to 2,000 μm.
 6. Thegelating agent for an alkaline cell according to claim 2, wherein thesoluble component amount of the gelating agent in ithe aqueous solutionis 0 to 30% by weight when the gelating agent is swollen in an aqueouspotassium hydroxide solution of 10% by weight concentration.
 7. Thegelating agent for an alkaline cell according to claim 2, wherein thepolymer (A) is obtained by polymerizing a monomer mainly (meth)acrylicacid and/or its alkali metal salt with neutralization degree of 0 to 30%by mole and further neutralizing the polymer based on the necessityafter polymerization.
 8. The gelating agent for an alkaline cellaccording to claim 1, wherein the swollen particle satisfying therequired condition (1) has particle size of 500 to 2,000 μm.
 9. Thegelating agent for an alkaline cell according to claim 1, wherein thesoluble component amount of the gelating agent in the aqueous solutionis 0 to 30% by weight when the gelating agent is swollen in an aqueouspotassium hydroxide solution of 10% by weight concentration.
 10. Thegelating agent for an alkaline cell according to claim 1, wherein thepolymer (A) is obtained by polymerizing a monomer mainly (meth)acrylicacid and/or its alkali metal salt with neutralization degree of 0 to 30%by mole and further neutralizing the polymer based on the necessityafter polymerization.
 11. The gelating agent for an alkaline cellaccording to claim 1 obtained by carrying out permeation drying and/orventilation drying after segmentation of water-containing gel based onthe necessity in the process of drying the water-containing gel of thepolymer (A) or by carrying out vacuum drying and/or ventilation dryingafter solid-liquid separation of the water-containing gel.
 12. Analkaline cell comprising an alkaline electrolytic solution containing azinc powder as an anode, wherein the gelating agent for an alkaline cellas claimed in claim 1 is added in 0.5 to 10% by weight to the weight ofthe alkaline electrolytic solution.
 13. An alkaline cell comprising analkaline electrolytic solution containing a zinc powder as an anode,wherein the cell contains a gelating agent, as claimed in either claim 1or claim 2, which is of a cross-linked polymer (A) comprising(meth)acrylic acid and/or its alkali metal salt as a main constituentmonomer unit, obtained by an aqueous solution polymerization or areversed phase suspension polymerization, useful for an alkaline celland satisfies the following required conditions (1) to (4): requiredcondition (1); that the gelating agent contains 50% by weight or more ofa particle whose swollen particle size becomes 300 to 4,000 μm when thegelating agent is swollen in an aqueous potassium hydroxide solution of40% by weight concentration; required condition (2); that the aqueouspotassium hydroxide solution of 40% by weight concentration containing3% by weight of the gelating agent has 0 to 20 mm stringiness; requiredcondition (3); that the aqueous potassium hydroxide solution of 40% byweight concentration containing 3% by weight of the gelating agent hasviscosity of 50 to 2,000 Pa.s at 40° C. after one day and sixty days;and required condition (4); that the gelating agent contains 0 to 15 ppmof a metal with a lower ionization tendency than zinc.
 14. The alkalinecell according to claim 13, wherein the polymer (A) is a cross-linkedpolymer with 5,000 to 1,000,000 average polymerization degree andcross-linked by an allyl ether type cross-linking agent (b) having 2 to10 of allyl groups in a molecule and the cross-linking agent (b) isadded in 0.05 to 1.0% by weight to the total weight of the (meth)acrylicacid and/or its alkali metal salt.
 15. A swelling-in-water type gelatingagent of a cross-linked polymer (A′) obtained by cross-linking a polymerwhich comprises (meth)acrylic acid and/or its alkali metal salt as amain constituent monomer unit, has 5,000 to 1,000,000 averagepolymerization degree and is produced by an aqueous solutionpolymerization or a reversed phase suspension polymerization, with anallyl ether type cross-linking agent (b) having 2 to 10 of allyl groupsin a molecule and added in 0.05 to 1.0% by weight to the total weight ofthe (meth)acrylic acid and/or its alkali metal salt, wherein thegelating agent is for an alkaline cell and satisfies the followingrequired conditions (1) to (4): required condition (1); that thegelating agent contains 50% by weight or more of a particle whoseswollen particle size becomes 300 to 4,000 μm when the gelating agent isswollen in an aqueous potassium hydroxide solution of 40% by weightconcentration; required condition (2); that the aqueous potassiumhydroxide solution of 40% by weight concentration containing 3% byweight of the gelating agent has 0 to 20 mm stringiness; requiredcondition (3); that the aqueous potassium hydroxide solution of 40% byweight concentration containing 3% by weight of the gelating agent hasviscosity of 50 to 1,000 Pa.s at 40° C. after one day and sixty days;and required condition (4); that the gelating agent contains 0 to 15 ppmof a metal with a lower ionization tendency than zinc.
 16. The gelatingagent for an alkaline cell according to claim 15, wherein the swollenparticle satisfying the required condition (1) has particle size of 500to 2,000 μm.
 17. The gelating agent for an alkaline cell according toclaim 15 containing 0 to 30% by weight of soluble components in anaqueous potassium hydroxide solution of 10% by weight concentration whenthe gelating agent is swollen in the said aqueous solution.
 18. Thegelating agent for an alkaline cell according to claim 15, wherein thepolymer (A′) is obtained by polymerizing a monomer mainly (meth)acrylicacid and/or its alkali metal salt with neutralization degree of 0 to 30%by mole and neutralizing the polymer based on the necessity afterpolymerization.
 19. The gelating agent for an alkaline cell according toclaim 15 obtained by carrying out permeation drying and/or ventilationdrying after segmentation of water-containing gel based on the necessityin the process of drying the water-containing gel of the polymer (A′) orcarrying out vacuum drying and/or ventilation drying after solid-liquidseparation of the water-containing gel.